(1) Field of the Invention
The present invention relates to an apparatus for inspecting for defects in small size objects such as tablets and the like, while the object is being conveyed by a conveyor.
(2) Description of the Related Art
As an example of conventional apparatus for this purpose, one of a number of various methods that have been proposed is that disclosed in Japanese Examined Patent Publication No. 5-65405. This method involves forming a slit serving as a suction opening and providing a pair of cables which are individually guided by guide rails formed on edge portions on opposite sides of the slit. Objects being inspected are placed on the cables and conveyed while being held by a negative pressure applied via the slit, and at a predetermined location the objects are photographed to thereby carry out inspection.
With such conventional arrangements however, the following various problems arise.
In practice it is difficult to form the slit by punching a single metal plate. More specifically, since the opposite sides of the slit are only bridged at the opposite ends, then even with a very rigid metal plate, it is difficult to maintain the opposite faces of the slit in the same plane, and hence a step difference in level across the slit cannot be avoided.
The slit is therefore formed for example by matching the edges of two thick very rigid plates. In this case however, extremely high manufacturing and assembly accuracy is required, incurring a significant increase in manufacturing cost merely for forming the slit. Moreover, maintenance is required to properly maintain the slit accuracy during use.
Furthermore, since normally the cables are positioned outside the slit forming the guide rails, then if a fragment from the object gets caught in the slit so as to protrude above the cables, then the objects being inspected are bumped by the fragment, the impact being sufficient to cause displacement and vibration of the objects. Hence an error occurs in the photographing inspection. Moreover, the photographing is carried out at a predetermined location, and if a fragment gets caught in the slit at the photographing location, then the fragment is photographed by the camera device so that there is the likelihood of an inspection error. Now as well as having a method wherein the object is photographed by the camera device over its whole surface, there is a method using a line sensor wherein back and forth scanning is repeatedly carried out in a straight line normal to the conveying direction, and the linearly scanned image is joined in a time series to give a surface image. With the former surface photographing method, due to the timing of the camera, when the object is photographed with a fragment lying on top, an inspection error occurs. With the latter linear scanning method, if there is a fragment lying on the scanning line, then since the fragment remains stationary, the fragment is photographed continuously, so that the resultant image of the object surface shows a streak having the same width as the fragment. There is thus the likelihood of an inspection error. Moreover, with both the surface photographing and the linear scanning method, even if a fragment gets caught away from but in the vicinity of the photographing region, then the caught fragment causes an obstruction which weakens the negative pressure applied to the object via the gap between the cables. Therefore in the case where the inspection object is a round tablet or the like, when it passes the caught fragment region, at first when the front side is above the caught fragment, the rear side is sucked with a relatively strong negative pressure so that the object inclines rearwards, then when the rear side is above the caught fragment, the front side is sucked strongly so that the object inclines forward. This results in a significant vibration so that here again inspection errors occur.
The above cases have been for when a fragment is close to the photographing location. However a problem which has a much greater probability of occurring is that with objects such as tablets, wherein fragments of the object are crushed finely into a powder which becomes attached to the inside of the slit. The occurrence of this powder is difficult to avoid with tablets and the like, and once conveying has continued for more than a certain duration the resultant quantity of powder becomes significant, evenly attaching over the whole inner wall of the slit, that is to say, also including the scanning location. In this case, with both the surface photographing method, and the linear scanning method, the powder attached to the inner wall of the slit is photographed as parallel streaks, so that there is a high possibility of considering this to be a defect in the tablet, in particular a fracture or a scratch. Hence inspection errors occur.
With the above described inspection errors due to the catching of fragments or to the attachment of powder in the vicinity of the photographing location, since these errors occur similarly for all of the objects being inspected, then once they arise practical inspection becomes impossible, and inspection is thus stopped. The fragment must then be cleared away or the powder removed, causing major problems.
In addition, the powder from the object can easily enter between the cables and the guide rails. In this case slipping of the cables can occur, and as well as being a source of inspection errors, this rubs against the cables and the guide rail faces, resulting in problems with endurance.
Now briefly considering the situation wherein the cables are fitted so that their edges protrude in from the edges of the slit forming the guide rails. In this case, since the gap between the cables is smaller than the gap of the slit, then fragments falling from the gap between the cables fall down without being caught by the slit, and fragments caught between the pair of cables are carried along as is. These can then be removed by providing a removal device such as a rotating brush downstream. Moreover, the attachment of powder to the slit wall, and the ingress of powder between the cables and the guide rails can be prevented to some degree. However in fitting the cables so that their edges protrude in from the edges of the slit, since, to ensure stable conveying, the cables must be tensioned by a certain amount so as to press against the guide rail, and since the protruding portion is subjected to the low negative suction pressure from the slit, then the same portions of the cable are continually pressed fairly hard against the edges of the slit resulting in rubbing. Therefore, there is significant deterioration and in practice from an endurance point of view this arrangement cannot be adopted.
Moreover, with slipping of the conveyor cables on the drive pulleys, a difference occurs in the conveying time from a scanning location to a sorting location where sorting is carried out based on the inspection results. Hence there is the possibility of erroneous sort.
Moreover, the slipping of the two cables can be different from each other. In this case there is the possibility of the object being rotated in a horizontal plane, resulting in a drop in the reliability of the inspection results. Alternatively, there is the situation wherein the cables rotate or twist about their axes. In this case, the object can drop into the slit so that there is the possibility of an erroneous judgement of object damage based on the inspection result.